Purification of cobalt precipitates containing iron and other impurities



Jan. 16, 1945. L. s. RENzoNl PURIFICATION 0F COBALT PRECIPITATES CONTAINING IRON AND OTHER IMPURITIES l Filed Jan. 15. 1943 y' mgm ATTORNEY .lead andr nickel.

' Patented JmL-51e,` 194sv ITIES o'rnna Louis Secondo Renzoni, Port Colborne, Ontario,

Canada, assignor of Delaware 'to The International 'Nickel .Company, Incl, New York, N. Y., a corporation Application January 15, 1943, seriai'No.- 472,472

In Canada l The present invention relates to the lpurification lof cobalt precipitates containing iron,1.cobalt nickel and other impurities, and more particu- -larly to' the purification and recovery Vof high grade .cobalt from precipitates obtained vvin thepurication of electrolytes employed in the 'elec-1 trolytic refining of nickel. Such precipitates contain not only cobalt, but also copper, iron, arsenic,

Heretofore it 'has 'been customary when 'elecl tro-renning nickel to purify the electrolyte by j precipitation of various contaminants, such as iron, copperand cobalt.' In prior'V art operations the iron. and vthe copper have been removedby one process or another beforeany attempt has.

been' made to precipitate the cobalt and remove y the cobaltfrom'the nickel electrolyte.v Consequently,. the cobalt 'precipitates ofpr'ior art 'procasses-have been devoid, or .substantially devoid, of ironor, at' the most, have contained only l or'2% of iron. Such cobalt precipitates-consisting 'primarilyof cobalt and nickel, have been produced in.prior art processes by oxidizing the c obalt with hypochlorite under carefully controlled conditions and precipitating the' cobalt in the highest state of -oxidation by meansof an alkali,

such' as sodium, or anA alkaline. earth, such as I calcium. In the conventional prior; art process,

and the precipitating alkali the oxidizing. agent were added to the electrolyte asia'hvpohlorite.

l Thus, .sodium hypochlorite andl calcium` hypovide? aj means to provide a 'f process ctober 16,1942 claims. (ci. 'z5-11o) for .purifying cobalt' precipitates containing 'appreciable amounts of iron' as well as arsenic, lead, copper and nickel whereby there is `obtaine'zd' a cobalt precipitate of sufficient purity to be satisfactory directly for industrial purposes.

-It is 'another object of the present invention to provide a means .for purifyingl cobalt precipitates containing lead, arsenic and appreciable amounts of iron in additionto nickel and copper, wherein the cobaltprecipitate is subjected to'the action of a reducing agent such as sulphur dioxide to solubilize the various metals present, followedby 4treatx'nent with anoxidizingagent to oxidize and precipitate thev,iron,lead and arsenic .substan tially devoidof cobalt.

It is a .further object of the present invention for removing. iron, arsenic, lead andv cobalt, together. with some copper, from nickel electrolytes to provide a partially Vpuriied nickel electrolyte ,and a precipitate containing substantially-- all the lcobalt present in the elec- A.trolyte tgetherwith lead, arsenic and large chlorite have been employed as oxidizing and precipitating agents for removing cobalt froni vari y ous solutions'.

Another process which has been employed has involved precipitation .of cobalt bythe addition of nickel peroxide. AThe nickel peroxide oxidizes by the nickel as a result of which the cobalt is precipitated as an oxide.

In all of the prior art processes, the cobalt pre` the cobalt and the cobalt in solution is .replaced cipitate hasfbeen purified by 'solution-in acids I and 're-precipitated with -alkali or an alkalinev agent or with sodium hypochlorite. However,

none of the processes known to the art has been employed to purify cobalt precipitates containing appreciable amounts of iron and, in addition,

arsenic and lead in amounts greater than usually consideredas traces. Thus, the art has been'c'on-v .y fronted with the problem of purifying .cobalt pref cipitates containing, in addition to nickel, large.

lution in which the amounts of 'iron and appreciable amounts of lead and arsenic. So 'far as it has been ascertained, no solutionhas been yprovided for this problem. It isan object of the present invention to protionsitis. possible t'o stop vpurified state amounts' of .iron and to recover cobalt ina highly substantially devoid of iron, arsenic,

lead'and .nickel from the aforesaid precipitate.

'The invention likewise contemplates the treatment 'of cobalt` precipitates containing'. arsenic,

lead, 'rel-ativelyrlarge amounts of iron, copper and nickel, with. areducing agent such as sulphur dioxide. Vfollowed by 'treatment with an oxidizing agent such'as further ,amounts ofthe first cobalt precipitate an`d subsequent. separationof the iron to leave va solution substantially devoid of iron, arsenic and lead. l v

Other objects and advantages will become apparent from the. following description taken in conjunction with the-iigure which depicts in a more ci' less diagrammatic manner the ow. sheet of a procesador recovering cobalt by precipita tion from an aqueous solutioncontaining cobalt andpurifying the cobalt precipitate soobtained in accordance .with the present invention.

Broadlystated, the purification of cobalt` precipitates containing arsenic, lead and relatively large amounts of iron together with copper and nickel involves a. treatment with a reducing agent and a solubilizing agent to produce a solower state of oxidation while thef-iron, .arsenic and' lead remain in the oxidized state. In the reduced state the nickel and cobalt are readily soluble at pH 4.5- whereas the iron, arsenic and lead arenot. .Under rigidly controlled condithe reaction at the point where only'cobalt and nickel are reduced nickel and cobalt arein the 2 asoman land in a state which for convenience is called the acid soluble state. At this point sumcient acid may be added toA convert the reduced hydroxides or acid soluble" hydroxides to soluble salts and thus obtain a solution relatively free from iron, arsenic and lead and containing about 7,5 to 80% oi' the total cobalt, nickel and copper However, to allow for ease of control andfor the highest possible metals recovery, it is preferred to allow the reduction reaction .to proceed beyond this stage andlto reduce some of the copper. and iron and then to add suicient acid to dissolve the slime completely. rAfter complete solution of the slime at pH 1.5 to 2.0, the solution contains cobaltous, nickelous, cuprous and cupric and ferrous ions and some cuprous sullite separates out as a salt. This solution will selectively reduce and dissolve cobalt and nickel from an additional quantity of primary slime due to the reducing action ofthe cuprous sulte and ferrous ions. Thus the sulfur dioxide consumed for the reduction of iron and copper is not lost since the ferrous and cuprous ions in turn act as selective reducing agents toward the cobalt and nickel contained in the primary slime. As the nickel and cobalt are reduced and enter solution, the ferrous and cuprous ions are oxidized, the pH rises, and under proper conditions the iron is completely hydrolyzed. Arsenic and lead are precipitated with iron, and the result is a solution of cobalt, nickel and copper, essentially free from iron, arsenic and lead. The copper is removed by cementation to leave a solution containing practically no copper and containing 98% of the cobali; and nickel of the original precipitate'. The cobalt is recovered from the solution of cobalt and nickel salts by oxidation with a hypochlorite and precipitation with an alkali. It is well known that by careful operation a cobalt precipitate of high purity can be obtained from a solution containing practically nothing but cobalt and nickel salts. However, under such conditions, an appreciable amount of cobalt remains in solution. n the other hand, all of the cobaltA can be precipitated, but a certain amount of nickel is re-precipitated. It'is preferred to add suflicient hypochlorite and precipitating agent to precipitate all the cobalt, together with a small amount of nickel. and to purify this precipitate by reduction with a reducing agent and solution in acid followed by re-precipitation with hypochlorite and alkali until a cobalt precipitate of required purity is obtained.

The ilow sheet of'the drawing\ is illustrative of the .steps of obtaining a cobalt precipitate from an aqueous solution containing cobalt, nickel, iron, copper, arsenic and lead and the purication of that precipitate to obtain high grade cobalt. Thus, an aqueous solution containing nickel and at least some cobalt, iron, arsenic and lead in the reduced state is treated with oxygen containing gas selected from the group consisting of oxygen and air to obtain a reaction mass containing iron in the oxidized state. The reaction mass containing iron in the oxidized state is then treated with chlorine to obtain a reaction mass containing cobalt, lead and arsenic together with iron in the oxidized state. I'he pH oi' the mass is adjusted to permit the iron salts to hydrolyze and precipitate the iron as the hydroxide or hydrated oxide. 'I'his is conveniently done by adding alkali. Cobalt, copper, nickel, lead and arsenic likewise precipitate and form 'a flrst precipitate containing cobalt, iron, arsenic, lead, copper and nickel. 'I'he ilrst precipitate is suspended in an aqueous medium and sumcient sulfur dioxide is introduced into said aqueous mediumv to reduce practically all of the cobalt and nickel and at least a part of the iron. Sum'cient sulfuric acid is then added to the aqueous medium to bring the pH of the aqueous medium to below about pH 2.0 to obtain an aqueous medium containing soluble salts o1' cobalt, nickel and iron in the reduced state together with compounds of cop per. To this aqueous medium containing soluble salts of cobalt. nickel and iron in the reduced state suihcient of anoxidizing agent, preferably the iirst precipita is added to oxidize the reduced iron, but not the cobalt and nickel and to provide a solution having a pH of about pH 4.5 in which-practically all of the iron is present in the oxidized state and practically all of the cobalt and nickel are present as soluble salts of reduced cobalt and nickel. At pH 4.5 the oxidized iron will hydrolyze to form a precipitate of oxidized iron, lead and arsenic. This precipitate rof oxidized iron, lead and arsenic is separated from the aqueous medium and washed with water. 'Ihe wash water is combined with the aqueous medium. The aqueous medium now contains the sulfates of cobalt, nickel and cop- Der. This solution of sulfates of cobalt and nickel in the reduced state and of copper is then treated with nickel powder to cement out the copper which is separated from the solution of cobalt and nickel sulfate in the reduced state.

'I'he solution of reduced cobalt and nickel salts is then treated with an` oxidizing agent such as sodium hypochlorite which precipitates the cobalt. The cobalt precipitate is separated from the nickel sulfate solution which is returned to the rst step o1' the operation. The precipitate of cobalt contains about 2.4% nickel and is treated with a reducing agent such as sulfur dioxide and taken into solution with sulfuric acid. 'I'he solution of cobalt sulfate and nickel sulfate is then treated with an oxidizing agent such as sodium hypochlorite and the cobalt again precipitated. 'Ihis cobalt precipitate only contains about 0.4% to about 0.6% nickel. This low nickel cobalt precipitate is washed with water and the wash water returned to the rst step of the operation. 'I'he washed cobalt precipitate is then roasted at a temperature not greaterfthan about 2100 F. to obtain a cobalt oxide. This cobalt oxide is leached with water to remove water soluble sulfur salts and produce a cobalt oxide which on drying assays about '70% cobalt and about 0.8% nickel.

'I'he following is an illustrative example of the application of the principles of the present invention to the treatment 'of a cobalt precipitate containing relatively large amounts of iron.

A cobalt precipitate having the following composition was treated 'in the following manner:

Constituents About 14.

About 876 pounds of primary cobalt slime having the composition set forth hereinbefore was suspended in 25 cubic feet of water at 100 F. and' SO2 was passed into the suspension until the pH-,reached a. value of about 4.5. This required that about 120 pounds of sulfur dioxide be introduced into thesuspension in a period of about hours, during which time the tempera- However', after 120 pounds of SO2 had been added, the pH of the suspension was about the same as at the beginning of the treatment, to wit, about was carried out atpH 2.3 and 100 F. until theA pH 4.5. After 120 pounds of SO2 had been added to the solution, about 200 pounds of sulphuricv acid.(66 Baum) were added and the pH of the resulting solution was about 1.5. Thereafter, about 165 pounds of primarycobalt slime having the composition set forth hereinbefore was added to the solution and thel temperature raised to about 180 about 4.5 andthe iron was precipitated, probably as `ferric hydroxide. The ferric hydroxide was removed by filtration and the ferrie slime washed with water. The washings were combined with the original filtrate and the total solution had the following composition:

F. The pH of the suspension rose toresidual cobalt content `of the solutionwas reduced to about 0.2 grams per liter. The cobalt precipitate produced contained 53 to 55 per cent cobalt and .2 to 4 per cent nickel. The precipitate was allowed .to settle and the supernatant nickel solution decanted. The

the action of sulfur dioxide and sulfuric acid, the pH of the resulting solution being about 2.0. -This solution was obtained substantially devoid of dissolved sulfur dioxide by adding 42 pounds of acid after 34 pounds of sulfur dioxide had been added to the suspension ofthe first cobalt slime. The cobalt was precipitated from this solution by the addition of alkaline hypochlorite and washed twice, preferably by'decantation, after which it was filtered The second cobalt slime contained 55 to 57% cobalt and about 0.4 to about 0.6% nickel. The solution from which the second-cobalt slime was precipitated had a residual cobalt contentl of about 0.2 gram per liter. This second cobalt slime was then roasted at a maximum` temperature of 2100 F. and the roasted product i Constituents Grmsprliter leached to remove soluble sulfur salts. The product produced by roasting and leaching had the Iron About 0.001 in o o ii nz. Copper. About 5.2 follow g c mp s to Nickel About 2&0 C0ba1t About 2o-0 Constituents Per cent The'ferr'ic slime had the following composition: About 7o l About 0 80 About o 2s Constituents Percent About 0.003 Iron About 38 n Abmt 0001 gregge# e 011@ gg u O a cgimelp... boat 1 5 40 Similar products containing 70% cobalt, 0.6 to AISBQIC About 3-5 0.8% nickel and 0.2% iron, 0.1% copper and 0.2%

The iron-free solution comprising the filtrate and washings from the ferrie slime was treated for the removal of copper by cementation, preferably with gas-reduced,nickelpowdeix ,A iiltrate was obtained containing: A.

Constituents Grams per liter About 0.003 About 0.001 About About 20 In the event'thatthe gas-reduced nickel contains a small amount of iron, it is desirable, and in fact essential, to aerate the filtrate from the copper'cementation to precipitate any additional.

chlorine to soda ash in the proportion of about V1 pound of chlorine to about 3.90 poundsof soda ash. This provides a solution -containing about 87% of the theoretical quantity of alkali, i. e., a solution having a slightly lower than theoretical alkali to available chlorine ratio. The precipitation based on the following reaction,

Cul

manganese can be obtained by employing the principles of the present invention. A specific example, illustrative, but not restrictive of the operation of the present invention,'is

as follows: i

Considering the treatment of a primary cobaltbearing iron slime having the following composition About50 About 14.8 About 20.8 About 6.00 .About 5.9

About 0.56 About 0.10

876 pounds of 'the moist slime were suspendedv in 25 cubic feet of water at 100 F., and sulfur dioxide passed through the suspension until the pH reached. a value of 4.5. At this stage, 64.8 pounds of cobalt, 91 pounds of nickel, 12.1 pounds of copper, and 1.6 pounds of iron were in the reduced state, 24.7 pounds of iron remained i'n they oxidized state. added and the slime completely dissolved, the' iinal pH of the solution being 1.5. On standing,

crystals of cuprous sulphite separated from the solution. To this solution, pounds of primary slime was added andthe temperature was raised to 180 F. The cuprous sulflte and ferrous ions kpreferentially reduced the cobaltic-and nickellic hydroxides and rendered' cobalt precipitate l was re-suspended in water and re-dissolved by while 13.7 pounds of copper, and

200 pounds of sulfuric acid [were then an additional v them' soluble. At the same time lan equivalent amount of cupric and ierric ions were formed. The pH of the solution rose as a result of the dissolution of cobalt and nickel, and substantially complete iron hydrolysis took place. Under the strongly oxidizing conditions, arsenic and lead were also oxidized and co-precipitated with the iron. The result was a solution containing about 98% of the total cobalt, about 98% of the total nickel and about 82% of the total copper, and a secondary iron slime containing practically all of the iron, arsenic and lead.

The reactions involved in the treatment Yo! the slime may be expressed as follows:

(I) Reduction of cobalt and nickel with sulfur dioxide. y

2Go OH) a -i-SOz-*COSOH-Co (OH) :+2H2O Nickel plus cobaltis expressed as cobalt. (II) Reduction of copper.

(b) CuzSO4+SOz+HzO Cu2SOa+HzSO4 (III) Reduction of iron.

(IV) Upon the additon ofsulfuric acid, the reduced cobalt, nickel and iron hydroxides were dissolved and ferrie hydroxide reacted with cuprous sulte as follows:

In all, 24.7 pounds of iron were reduced in this manner, and consequently 11.3 pounds of cuprous copper were oxidized.

After the addition of sulfuric acid, the following conditions existed in the solution: pH 1.5, Co++ 64.8 pounds, Ni++ 91.2 pounds, Fe-il-i- 26.3 pounds, Cu-l--l- 25.0 pounds, Cuz-l--l-l 0.8 pound.

To oxidize and hydrolyze all of the iron, and to utilize the reducing properties of the solution, an additional 163.16v pounds of primary slimes were required, 'and tained therein entered the solution as follows: (I) Reduction by cuprous sulte followed by a rise in solution pH; and (II) Reduction by ferrous ions followed by iron hydrolysis to form ferriev hydroxide.

'I'he dried slime contained 35.6% nickel plus cobalt,.which for this purpose may be considered as being all cobalt. Acid neutralized in raising the pH from 1.5`to 4.5=3.0 pounds I-IzSO4. The acid was neutralizedaccording to the followin-g reaction:

copper.

Dried slime required 4.08 pounds. Wet slime requred=8.16 pounds slime.

Weight of iron to be oxidized and hydrolyzed=26.3 pounds.

Cobalt and nickel required by the following reaction,

Weight or wet slime required-zl-sxhiss pounds slime.

'rom weight traum@ to be uddt`u=1sa-1e pounds.

the nickel and cobalt conaaemao From the foregoing it is clear that if the reduction with sulfur dioxide is carried beyond the complete reduction of cobalt and nickel, a certain minimum cuprous copper content is required at the time of acid addition. 'I'his is equivalent to approximately 0.5 times the iron present as ferrie hydroxide. With this amount of cuprous copper present, the iron is completely reduced upon acid addition, and suicient cuprous suliite remains to allow the pH to rise from 1.5 to 4.5 upon the addition of a suiiicient quantity of primary iron slime. If lesser amounts of cuprous copper are present the pH of the solution will not rise to the value required for complete iron hydrolysis. If larger amounts of cuprous copper are present, no problem is presented since the pH may be kept at the proper value by acid additions.

Although the present invention has been described in conjunction with certain specific embodiments thereof, it is to be understood that the primary cobalt slimes may have a composition within the following range:

Constituents Percentages About 6 to about l5 About 0.3 to about 0.7 About 0.1 to about 0.2 About 0. l to about 0. 2 About 3 to about l0 About 16 to about Z5 About 5 to about l5 Constituents Grams per liter About 0.001 toabout 0.005 About 0.0001 to about 0.0000 About 0.0001 to about 0. 0005 About 0.03 to about 0.05

About 2 tn about l0 About 30 to about 40 About 2l to about 25 The cement copperl will have a composition a composition falling within the following range:

Grams per liter The rst puried cobalt slime will have a composition falling within the following range:

Constituents Percentages About 0.08 to about 0. in About 2 to about 4 About 53 to about 55 The iiltrate from the first purified cobalt slimes at which ferric salts asemee About 20 to about 30 About 0. l to about 0. 5

/- I vThe purined roasted product will have a composition falling within the following range:

Constituents Percentages Cobalt oxide About 70 r to about 7l Nickel oxide-. About 0.6 to about 0.8 Iron About 0.1 toabout 0.2 Copper.. About 0.01 toabout l0 Sulfur-- About 0.02 toabout 0.03 Arsenic- About 0.001 to about 0.003 Lead About 0.0005120 about 0.001

In carrying out the process described hereinbefore, it has been possible lto recover about 94 per cent to about 96 per cent ofthe cobalt present in the original impure cobalt slimes.

The -present invention provides a process which is of particular importance to the electrolytic rening of nickel. It has been found that by precipitating the iron, lead, arsenic and cobalt simultaneously, electrolytic nickel containing not more than 1% per cent cobalt can be produced. Although the present invention has been described in conjunction with certain preferred embodiments thereof, those skilled in the art will readily understand that modilications and variations thereof can be made. Such modications and variations are to be considered within the purview of the specification and the scope of the appended claims. I claim: f 1. A process for recovering cobalt from cobaltcontaining material having nickel and appreciable amounts of iron and copper present which comprises making an aqueous suspensionof material containing cobalt, nickel, iron and copper in the oxidized state, introducing sulfur dioxide into said suspension inA amount sufficient to reduce practically all of the cobalt and nickel compounds and at least a part of the iron therein, adding sufficient of a strong mineral acid to dissolve said reduced cobalt and nickel compounds and to form a solution containing cobalt and nickel salts, introducing into said solution suincient material containing iron, cobalt and nickel in the oxidized state to oxidizethe reduced iron but not the cobalt and nickel to oxidize the iron and to raise the pH of said solution to that pH hydrolyze, hydrolyzing the oxidized iron to obtain an aqueous suspension of a precipitate .of iron, separating said iron precipitate from said aqueous suspensionto provide a solution containing copper, cobalt and nickel, removing copper from said solution by cementation to obtain a solution substantially devoid of iron and copper and containing substantially all of the cobalt and nickel, and recovering cobalt containing only small amounts of nickel and substantialiy devoid of iron and copper.

2. A process for recovering cobalt from material containing nickel, copper and appreciable amounts of iron Awhich comprises making an aqueous suspension of material containing cobalt, nickel, iron and copper in the oxidized state, in-

' troducing sulfur dioxide into said suspension in amount sufficient to reduce practically all of the cobalt and nickel compounds and at least a part of the iron compounds, adding sufficient of a strong mineral acid to dissolve said reduced cobalt and nickel compounds and to form a solution containing cobalt-and nickel salts, adding sufficient material containing iron, cobalt and nickel'in the oxidized state to oxidize the reduced iron but not thecobalt andl nickel, raising the pH offsaid solution to a pH at which ferrie salts hydrolyze, hydrolyzing the oxidized iron to obtain an aqueous solution containing a precipitate of iron, separating said iron precipitate.v from said aqueous suspension to provide a solution containing nickel, cobalt and copper, removing copper by cementation to obtain a solution containing cobalt and nickel salts substantially devoid of iron and copper, oxidizing at least a major portion o said cobalt, precipitating said oxidized cobalt contaminated with nickel, separating said contaminated cobaltfrom the solution, and purilying said contaminated cobalt to obtain a cobaltcontaining material substantially devoid of iron and copper and containing not more than about 1% of nickel.

3. A process for recovering cobalt from material containing cobalt, nickel, -copper and more than traces of iron in the oxidized state which comprises making an aqueous suspension of material containing cobalt, nickel, iron and copper in the oxidized state, introducing sulfurous anhydride into said suspension in amount sufllcient to reduce all of a portion of the iron, strong acid into said solution to provide a pH not higher than about pH 2.0 to dissolve the reduced cobalt and nickel, adding suilicient material containingL iron, cobalt and nickel in the oxidized state to oxidizesaid reduced iron but not the cobalt and nick'el in said solution having a pH not greater than about pH 2.0, raising the pH of said solution to that pH at which ferrie salts hydrolyze, hydrolyzing the oxidized iron 'to obtain an aqueous suspension containing a precipitate of iron, separating said iron precipitate from said aqueous suspension to obtain an aqueous solution substantially devoid of iron and containing cobalt, nickel and copper, removing copper from said solution by cementation to obtain an aqueous solution substantially devoid of iron and copper, and recovering cobalt containing only small amounts of nickel.

-4. A process for recovering cobalt from material containing cobalt, nickel, copper and more vto below about pH 2.0

than traces of iron which comprises making an aqueous suspension of material containing cobalt, nickel, copper and appreciable amounts of iron inthe oxidized state, introducing sulfur dioxide into said suspension until at least a portion of the iron is reduced together with practically all ol. the cobalt and nickel, adding sufficient sulfuric acid to bring the pH of the aqueous suspens-ion to provide a solution containing reduced iron, cobalt and nickel, introducing suflicient material containing iron, cobalt andv nickel in the oxidized state t0 oxidize said reduced iron, but to leave the cobalt and nickel in the reduced state to obtain a reaction mass having a pH not greater than about pH 4.5 in which practically all of the iron is in the oxidized state and practically all oi the cobalt and nickel are present as soluble salts of cobalt and nickel in the vreduced state, hydrolyzing the oxidized iron compound to obtain a suspension containing a precipitate of iron, separating said iron precipitate from said suspension to obtain a solution substantially devoid of iron and containing soluthe cobalt and nickel and at least y introducing suicient of ay Aoxygen-containing gas selected fro mass containing cobalt, lead and arsenic together with iron in the oxidized state, hydrolyzing said oxidized iron to obtain a reaction mass containing a first precipitate of cobalt, iron, arsenic, lead, copper and nickel; suspending said precipitate in an aqueous medium, introducing sulcient sulfur dioxide into said aqueous medium to reduce practically al1 of the cobalt and nickel and at least a part of the iron; adding sumcient sulfuric asoman acid to said aqueous medium to bring the pH of said aqueous medium to below about pH 2.0 to obtain an aqueous mediurmcontaining soluble salts of cobalt, nickel and iron in the reduced state together with compounds of copper; adding sucient of an oxidizing agent comprising said iirst precipitate to oxidize the reduced iron but not the cobalt and nickel, to provide a solution having a pH of about pH 4.5 in which practically all of the iron is present in the oxidized state and practicallyall of the cobalt and nickel are present as soluble salts of reduced cobalt and nickel; hydrolyzing said oxidized iron to obtain a precipitate of oxidized iron, lead and arsenic; separating said precipitate containing iron. lead and arsenic from said aqueous medium to obtain a solution containing cobalt and nickel in the reduced state and copper; removing copper from sai'` solution to obtain a solution of cobalt and nickel in the reduced state substantially devoid of copper, iron, lead and arsenic; and recovering cobalt containing only small amountsof nickel.

` LOUIS SECONDO RENZONI. 

